1. Field of the Invention
The present invention relates to compositions of mixed hyaluronic acid (“HA”) copolymer gels containing at least one silicone base polymer, formulations containing them, and a method of preparation.
2. Description of the Related Art
Zhao, et al., U.S. Pat. No. 6,703,444 discloses cross-linked HA derivatives, wherein the HA is cross-linked with one or more polymers other than HA having two or more functional groups capable of being covalently bonded with HA to form a product having at least two chemically distinct covalent cross-links between HA and the said polymers. Balazs, et al., U.S. Pat. No. 4,582,865 describes the preparation of cross-linked gels of HA by cross-linking HA by itself or with other hydrophilic polymers using divinyl sulfone as the cross-linking agent.
By way of background, it should be noted that hyaluronic acid (HA) and its derivatives are important materials used in the medical and cosmetic industries. Its unique viscoelastic properties combined with its high water binding properties and exceptional biocompatibility have led to a wide variety of products in the ophthalmic, arthritis, wound healing, anti-adhesion, drug delivery, soft tissue augmentation, burn management, and topical cosmetic moisturization fields. Cross-linking of HA has long been used to improve the physical properties of the molecule and to enhance the properties for various uses, or to immobilize the HA to various supports for medical purposes including the diagnosis of male infertility. Formulations of HA have been used in the cosmetic industry as skin moisturizers. Since HA and its salts have similar properties we will refer to them interchangeably as hyaluronic acid or HA. HA is a naturally occurring polysaccharide consisting of alternating N-acetyl-D-glucosamine and D-glucuronic acid monosaccharide units linked with alternating β1-3 glucoronidic and β1-4 glucosaminidic bonds. The molecular weight of hyaluronic acid is generally within the range of 50,000 up to more than 8,000,000. HA is found in all vertebrates in large quantities in the skin, vitreous humor, the synovium, the cartilage, and the umbilical cord. It is not species specific and is therefore highly biocompatible. It is known for its efficiency of hydration, it has a binding capacity of up to 20 times its weight in water; it is the natural moisturizer in the cell matrix of the skin; and it exists at concentrations of 200 microgms per gm of dermal tissue.